1. Field of the Invention
The present invention relates generally to the field of biasing and actuator devices for electrical switches, disconnects, contactors and the like. More particularly, the invention relates to an innovative biasing structure incorporating rolling elements for shifting an actuator between stable, biased positions by rolling contact of the rolling elements against one another. The invention also relates to a modular structure for attachment of the biasing assembly to a switching device.
2. Description of the Related Art
A variety of actuators and biasing arrangements are known and presently available for switching devices such as contactors, disconnects and the like. In general, such actuators may be manually or remotely operated, such as by a lever arm coupled to a rotary shaft. In one known family of disconnects, blade-type conducting elements are secured to a rotary shaft and are moved between conducting and non-conducting positions by rotation of the shaft. In the conducting position, the conductors complete current-carrying paths through the device. Such disconnects may include fuses such that, when installed, the device completes current-carrying paths through the fuses to a downstream load.
In order to avoid unnecessary heating and arcing in switching devices of the type described above, a rapid snap-action mechanism is generally associated with the device to urge the conductors rapidly into either their conducting or non-conducting position. In manually-operated devices, the mechanism is moved from its stable positions by movement of the manual actuating lever. The mechanism is pre-loaded by initial movement of the actuating lever and, once a predetermined intermediate position is reached, snaps or toggles from its first (e.g., non-conducting) position to its second (e.g., conducting) position. The mechanism operates in an opposite sense to rapidly shift the switching device back from the latter position to the first position when the lever is moved in an opposite direction.
Various forms of biasing mechanisms have been proposed in the art. Most mechanisms include some form of toggle which is pre-loaded by the initial movement of the actuating lever, and which moves rapidly to an over-center position under the influence of a compression or tension spring. The particular configuration of the biasing device, including lever arm lengths, pivot axis positions, spring coefficients and bearing surface areas combine to determine the force with which the biasing device must be pre-loaded and the corresponding force and speed with which the device snaps between its stable positions. In general, a balance must be struck between the physical size and weight of the biasing device and the forces required to actuate it and to stop the moving components once they arrive in the stable positions. Moreover, bearing surfaces and forces are particularly important in the design of the biasing devices insomuch as they have an important impact on the speed with which the device moves between the pre-loaded, intermediate position and the subsequent stable position.
While many known biasing devices for switches provide generally adequate reliability, they are not without drawbacks. In particular, due to the layout and construction of bearing surfaces in most known toggle-type structures, the speed of actuation is limited. While the speed could be increased by pre-loading the toggle with a higher coefficient (i.e., stiffer) biasing spring, the resulting pre-load forces and impact forces upon the actuator reaching the stable positions become unacceptably high. Such forces can be accommodated by either reconfiguring the entire mechanism or by providing much more robust, and consequently more expensive and heavy mechanical linkages, stops and bearings within the device. Moreover, while many industrial disconnects and similar switching devices offer the flexibility of mounting actuators on either side of their housings, known biasing devices do not provide sufficient modularity to permit them to be easily installed on either side of the device without some disassembly and reassembly.
There is a need, therefore, for an improved biasing mechanism for disconnects, contactors, and other switching devices which addresses and avoids these drawbacks. In particular, there is a need for an improved biasing device structure which effectively overcomes the limitations of existing devices with respect to bearing forces and surfaces, which otherwise limit the rapidity with which the device moves between its stable positions. There is also a need for such an improved biasing device configured in a modular structure which can be quickly and easily mounted to either side of a switching device without requiring extensive disassembly and reassembly.